The use of cleaning blades is widely practiced in electrostato-graphic printers and copiers for the removal of toner particles from various moving surfaces (Seino et al. J. Imag. Sci. & Tech. 2003, Vol. 47, 424). The portion of the cleaning blade that contacts the surface to be cleaned is generally a polyurethane because such polymers are durable and have a high degree of resilience that is well suited for making contact with a smooth surface.
The use of cleaning (wiper) blades for cleaning webs is described in U.S. Pat. No. 6,453,134 (Ziegelmuller et al.) where the cleaning blades are used to clean transport webs in electrophotographic printers. Toner patches are removed from the transport webs after image density is measured with some type of radiation such as a light emitting diode (LED).
The properties of such cleaning blades can be improved by surface coatings over the polyurethane. For example, U.S. Pat. No. 5,363,182 (Kuribayashi et al.) describes the use of a surface coating of graphite particles in a nylon resin. A primer layer is used to enhance the adhesion of the graphite-containing nylon resin to the polyurethane blade.
Urethane polymers that are designed to be hard like a ceramic yet flexible like a polymer are part of a group of materials known as ceramers. As discussed in U.S. Pat. No. 5,968,656 (Ezenyilimba et al.), ceramers are coated as layers of approximately 5 micrometers on relatively thick, resilient polyurethane substrates or cushion “blanket” cylinders to provide transfer of toner from a photoreceptor to a receiver in electrophotographic printers. One ceramer composition has a urethane backbone made from isophoronone diisocyanate and a polyether diol wherein the backbone is branched by the addition of trimethylolpropane and 1,4-butane diol serves as a chain extender, and the branched urethane is endcapped with 3-isocyanatopropyltriethoxysilane to provide alkoxysilane groups that can react with alkoxysilanes in a sol-gel reaction to form a polyurethane silicate hybrid organic-inorganic composite (OIC) network ceramer.
Urethane polymers containing fluorinated substituents are known. One mode of introduction of the fluorinated component is from a fluoroether, either as an endcapper or from the diol into the polyurethane backbone. U.S. Patent Application Publication 2007/0244289 (Tonge) describes a method of making urethane based fluorinated monomers that can be used to prepare radiation curable coating compositions, and discloses that such monomers can be used to formulate a ceramer composition such as disclosed in U.S. Pat. No. 6,238,798 (Kang et al.) that describes ceramer coating compositions comprising colloidal inorganic oxide particles and a free-radically curable binder precursor which comprises a fluorochemical component that further comprises at least two free-radically curable moieties and at least one fluorinated moiety. In such compositions, the colloidal inorganic oxide particles can be surface treated with a fluoro/silane component that comprises at least one hydrolysable silane moiety and at least one fluorinated moiety. As discussed therein, aggregation of the inorganic oxide particles in such compositions can result in precipitation of such particles or gelation of the ceramer composition, which, in turn, results in a dramatic, undesirable increase in viscosity.
Copending and commonly assigned U.S. Ser. No. 12/713,205 filed Feb. 26, 2010 by Ferrar, Rimai, Miskinis, and DeJesus describes cleaning blades having a polymer substrate and fluorinated polyurethane ceramer coatings that provide increased surface modulus with a low surface energy coatings. These improved cleaning blades represent an important advance in the development of cleaning systems, but there is a desire to further improve such cleaning systems.
Of particular interest is providing improved cleaning blades that can perform the cleaning function with minimal impact on the functionality and durability of the surface that is being cleaned by the cleaning blade. This is particularly important where the surface being cleaned is a primary imaging member of an electrophotographic printing system. Such a primary imaging member is designed and carefully manufactured to receive a generally uniform initial charge on an outer surface thereof, to selectively discharge initial charge to form an image modulated charge pattern when exposed to a pattern of light, to receive any toner that develops onto the outer surface in response to the charge pattern and to enable this toner pattern to be transferred intact onto a transfer member. Further, the primary imaging member also must be capable of being cleaned for example by a cleaning blade that scrapes or wipes toner and contaminant from the surface of the photoreceptor in a manner that enables the primary imaging member to repeat this cycle more than 100 times per minute for millions of cycles without perceptible degradation in function.
It will also be understood that while cleaning blades are primarily designed to provide effective cleaning of a primary imaging member it is also necessary that they do so while providing minimal interference with the functions of charging, selective discharging, and development. The cleaning blades further must perform the cleaning function in a manner that does not unduly reduce the number of cycles that a primary imaging member can be used.
For example, when a primary imaging member is cleaned by a cleaning blade, there is a risk that contact between the cleaning blade and the primary imaging member can create a charge on an outer surface of a primary imaging member because of the triboelectric effect. The triboelectric effect occurs where two materials are brought into contact that have, for example different electronegativity. In such a situation charge is transferred from one of the materials to the other.
The presence of a charge caused by the triboelectric effect can alter the charging and discharging properties of the primary imaging member. This creates areas of local charge variation that can prevent the primary imaging member from generating charge patterns that accurately reflect the imagewise exposure made on the photoconductor. Further, when an imagewise exposure of the photoreceptor to light occurs before the tribocharging induced charges are eliminated the tribocharging induced charges can be trapped in the primary imaging member in a way that cannot be eliminated.
Friction can also influence the performance of a primary imaging system and plays an important role in cleaning. When there is too much friction between a cleaning blade and the surface that the cleaning blade is cleaning, the cleaning blade can wear and heat the primary imaging member, as well as cause effects such as chatter, misregistration, and other effects known to those of skill in the art.
Two common types of friction reducing materials can be used to reduce friction between a cleaning blade and a surface that the blade is used to clean. The first type of friction reducing materials includes materials such as fluoropolymers such as Teflon. These materials are extremely electronegative and tend to charge primary imaging member positively when used as cleaning blades. The second type of friction reducing materials includes materials such as graphite whose crystal structure readily shears to reduce friction. However, materials such as graphite tend to be electrically conducting and can leave a conductive residue across portions of the surface being cleaned. The presence of such a conductive residue can interfere with charge patterns that must be provided on a primary imaging member to enable electrophotographic printing.
What is needed therefore is a cleaning system with controlled tribocharging and, optionally, controlled friction.